This invention relates to display arrangements and more particularly, but not exclusively, to helmet-mounted displays used by aircraft pilots.
In a conventional helmet-mounted display, a small cathode ray tube (CRT) is mounted on the helmet of the pilot or other member of the air crew. The electron beam of the CRT is scanned over its faceplate to generate an image. Specially designed relay optics interface with the CRT faceplate to convey the image into the field of view of the pilot, typically being presented on a combiner attached to the helmet. The relay optics are generally quite complex, involving several elements for focussing and directing the image, and require a significant degree of design effort to integrate them with the CRT and with the part of the system which the pilot actually views. For example, if the image is to be projected onto a visor, the curvature of the visor, which may present a complex optical surface, must be taken into account. Electrical cabling connects the CRT to the power supply and also includes an electrical path for applying control signals to the CRT for scanning the electron beam and modulating it with the required information.
The present invention seeks to provide an improved display arrangement which is particularly suitable for use in helmet-mounted displays but which could also have application in other fields and in non-military environments.
According to the invention, there is provided a display arrangement comprising: a display device having a screen at which an image is produced and means for optically relaying an image from the device for viewing by a user, the display device comprising a light source, means for modulating light from the source with image information and a scanner for scanning modulated light over the screen, the screen and scanner being head mounted.
By employing the invention, it is possible to provide to a user an image of the same or superior quality as would be achieved with a CRT-based display arrangement and also provide a number of advantages. A CRT display is located close to the user""s head and requires a high voltage supply. It also requires a relatively large and unwieldy umbilical cable to provide the electrical supply to the CRT. This leads to difficulties in adequately shielding the long run of cable to prevent electromagnetic interference effects. The size and weight of the umbilical may also inhibit the pilot""s head movements and can be particularly problematical where the aircraft is expected to undergo maneuvers involving high gravitational forces. Also, the designer must ensure that if a pilot is forced to eject from the aircraft, the umbilical will readily detach. In contrast, a display arrangement in accordance with the invention does not require a high voltage supply to produce an image on the screen. Preferably, the light source is remotely located from the user""s head and is connected to the scanner via fibre optic means. It may be sufficient to have only a single, mono-filament optical fibre connecting the light source and scanner. Thus, the potential danger of having a high voltage supply is avoided and the umbilical to supply the display arrangement is of considerably less weight than the HV supply of a conventional CRT arrangement, is less restrictive of head movement and easier to detach in the event of pilot ejection. Also, electromagnetic interference problems are greatly reduced. Any electrical supply to the light source can be much more easily shielded as it is compact and may be included in already existing shielding arrangements for other electrical systems in a cockpit.
Also, the head-mounted parts of a display arrangement in accordance with the invention can be made much lighter in weight than the CRT components and also occupy the same or a reduced volume as compared to a CRT. According to a particularly advantageous feature of the invention, a display apparatus includes an optical relay designed for use with a CRT and a display arrangement in accordance with the invention wherein the screen is located substantially in the position which would be occupied by a CRT faceplate if a CRT were included instead of the display arrangement. The display arrangement in accordance with the invention may be used as a straight replacement for the CRT of a previously designed and installed display arrangement. It is not therefore necessary to completely redesign the relay optics or other means for conveying the image to the user. Replacement may be carried out with very little disruption to the parts of the system already installed and the advantages which arise from using the invention may thus be incorporated into a previously existing, conventional arrangement with what is effectively a minor modification. The modification is also relatively inexpensive to implement as there is no significant redesign involved in installing it.
A further advantage arising from the invention is that the display may be a color display although, of course, monochrome may be provided. In normal helmet-mounted displays using CRTs, monochrome only is available because the shadow mask required for color cannot be accommodated in the small space available and also vibration can be a problem. Furthermore, a very bright display is required and this is difficult to achieve in small color CRT displays.
In a display arrangement in accordance with the invention, the light source may be a single laser or a single LED (light emitting diode). Modulation of the light may be implemented by using a modulated light source, for example, a modulated LED or miniature laser diode or by modulating light subsequent to its generation. In other embodiments, a plurality of lasers or a plurality of LEDs may be included or it may be desirable, in some arrangements, to have a combination of the two types of light source. The plurality of lasers and/or LEDs may emit light of different wavelengths to give a color display. The image produced for viewing by the user may include alphanumeric information, for example, data concerning an aircraft""s altitude, heading and velocity or other information concerning aircraft systems or weapon status, in the case of military aircraft. Alternatively, or in addition, the image may be a pictorial display, for example, giving a representation of the view outside the cockpit as sensed, for example, by infrared imagers or image intensifiers. Alternatively, such pictorial information may comprise map data, for example.
The scanner may be arranged to direct the light beam using, for example, electromagnetic, electro-mechanical or acousto-optic means. In the latter case, the scanner may be operable without requiring a direct electrical supply to be provided from the aircraft, control being by way of modulated light signals transmitted along an optical fibre link.
The screen of the display arrangements mounted on the helmet may, for example, be a plain glass plate or, for example, could be a dispersive hologram.
According to a feature of the invention, an aircraft cockpit includes a plurality of displays, at least one of which is a display arrangement in accordance with the invention mounted on a helmet and at least one other of which is a head-down or head-up display comprising a light source, means for modulating light from the source with image information and a scanner for scanning modulated light over a screen. Thus, by using this aspect of the invention, it is possible not only to replace the conventional CRT display mounted on the pilot""s helmet, but also at least one CRT found in other parts of the aircraft cockpit and preferably all of them include a similar display arrangement, thus eliminating CRT displays from the cockpit entirely, with the attendant advantages as discussed previously.